Chemistry A: Predicting and Identifying Reactions and Products

What are the main reactions of Alkanes?

Alkanes primarily undergo combustion and halogenation. In complete combustion, alkanes react with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O). In incomplete combustion, the process yields carbon monoxide (CO) or even elemental carbon (C) and water (H₂O) in extreme cases. Halogenation is a reaction where alkanes react with halogens (like chlorine or bromine) under UV light, resulting in the substitution of hydrogen atoms with halogen atoms.

What is the mechanism of Halogenation in Alkanes?

The mechanism of halogenation in alkanes occurs through a process called free radical substitution, which is a multi-step reaction involving: initiation (formation of free radicals from halogen molecules when exposed to UV light), propagation (the free radicals react with alkanes to substitute hydrogen atoms with halogens), and termination (recombination of free radicals leading to stable products).

What is Hydrohalogenation in Alkenes?

Hydrohalogenation is an addition reaction where hydrogen halides (HX, such as HCl or HBr) react with alkenes to form haloalkanes. This reaction adheres to Markovnikov's rule, whereby the hydrogen atom from HX bonds to the carbon with the greater number of hydrogen substituents, producing the more stable alkyl halide.

What is the significance of Markovnikov's rule in organic reactions?

Markovnikov's rule is a guiding principle in electrophilic addition reactions involving unsymmetrical alkenes, stating that the hydrogen atom from an adding reagent (like HX) attaches to the carbon atom of the alkene that has more hydrogen atoms (the more substituted carbon). This stabilization of the transition state leads to a major product that favors the formation of a more thermodynamically stable carbocation.

What are the oxidation products of Primary and Secondary Alcohols?

Primary alcohols can be oxidized first to aldehydes using mild oxidizing agents, and then further oxidized to carboxylic acids using strong oxidizing agents such as potassium dichromate (K₂Cr₂O₇) in acidic conditions. Secondary alcohols can only be oxidized to ketones by strong oxidants. Tertiary alcohols show resistance to oxidation due to the lack of a hydrogen atom on the carbon bonded to the hydroxyl (-OH) group.

What is the role of nucleophiles in the reactions of Haloalkanes?

In the context of haloalkanes, nucleophiles are species that donate an electron pair and participate in nucleophilic substitution reactions. They can replace the halogen (which acts as a leaving group) in haloalkanes, leading to the formation of alcohols (when OH⁻ is the nucleophile), amines (when NH₃ is used), or nitriles (when CN⁻ is introduced). This can occur via different mechanisms depending on the substrate.

What are the main reactions of Carboxylic Acids?

Carboxylic acids undergo several important reactions: they participate in neutralization reactions with bases to form salts and water; in esterification reactions, they react with alcohols to produce esters and water, requiring an acid catalyst. They can also be reduced to primary alcohols by reducing agents such as lithium aluminum hydride (LiAlH₄).

What do electrophilic substitution reactions involve in Aromatics?

Electrophilic substitution reactions in aromatic compounds, like benzene and its derivatives, involve the substitution of hydrogen atoms on the aromatic ring with electrophiles such as nitronium ion (NO₂⁺) or halogen cations. The reaction proceeds through the formation of a reactive arenium ion intermediate, which retains the aromatic character after the hydrogen substitution.

What is the reactivity trend of Alkali Metals in water?

Alkali metals react vigorously with water, resulting in the formation of alkaline metal hydroxides (e.g., NaOH) and hydrogen gas (H₂). The ease of this reaction increases as you move down the group from lithium to cesium, making cesium the most reactive with water, due to its larger atomic size and lower ionization energy.

What distinguishes the reactivity of Halogens in displacement reactions?

In displacement reactions, a more reactive halogen can displace a less reactive halogen from a halide solution. For instance, chlorine (Cl₂) can displace bromine (Br₂) from potassium bromide (KBr), producing potassium chloride (KCl) and bromine gas (Br₂). This reactivity trend reflects the decreasing ability of halogens to undergo this transformation as you move down the group.

What color changes indicate the formation of colored complex ions in Transition Metals?

Transition metals can form colored complex ions with ligands, which are molecules or ions that bond to the central metal atom. For example, the complex ion [Cu(H₂O)₆]²⁺ appears blue, while [Cu(NH₃)₄(H₂O)₂]²⁺ exhibits a deep blue color. The specific color observed is influenced by the nature of the ligands and the oxidation state of the metal.

What is the trend of acidity in Period 3 Oxides?

In Period 3, oxides can be categorized based on their acidic behavior: Basic oxides like Na₂O and MgO react with acids to form salts and water, while amphoteric oxide Al₂O₃ can react with both acids and bases. Acidic oxides, such as SiO₂, P₄O₁₀, and SO₃, react with bases to form salts and water. The trend indicates an increase in acidity across the period from left to right.